This invention relates to drive mechanisms for medical devices and, in particular embodiments, to a drive mechanism for a medication infusion pump that utilizes shape memory alloy wire to activate the drive motion.
Traditionally, drive mechanisms for medication infusion pumps have used a motor that rotates a lead screw that is connected to a carriage, and the carriage is advanced by rotation of the lead screw. For example, as the motor rotates the threads of the lead screw, corresponding threads on the carriage that are engaged with the lead screw threads, advance the carriage forward along the lead screw. Generally, the carriage is connected to a nut, or other engagement member, that is connected to a piston in a medication cartridge, which is advanced with the carriage to dispense medication through a catheter.
However, a drawback to lead screw mechanisms is that they require a complicated motor assembly and drive parts, making them costly to produce. In addition, the lead screw and drive motor contribute to a substantial portion of the weight and volume in a medical infusion pump.
It is an object of an embodiment of the present invention to provide an improved drive mechanism for a medication infusion pump, which obviates for practical purposes, the above mentioned limitations.
According to an embodiment of the invention, a drive mechanism for a medication delivery device includes a force receiving member, a force applying member and a shape memory actuator. The force applying member is operatively coupled to the force receiving member to cause relative movement to occur between the force receiving member and the force applying member so that the force receiving member is in a different position relative to the force applying member. The shape memory actuator is formed from a shape memory material and is operatively coupled to the force applying member. Preferably, the shape memory actuator is heat activated to distort the shape memory actuator from a first shape to a second shape to activate the force applying member to act upon the force receiving member to cause the relative movement between the force applying member and the force receiving member so that the force receiving member is in the different position relative to the force applying member. Also, the shape memory actuator is returned to the first shape from the second shape after the force receiving member is in the different position relative to the force applying member. In particular embodiments, the force applying member is stationary and the force receiving member is moved by the force applying member. In other embodiments, the force receiving member remains stationary and the force applying member is moved relative to the force receiving member. In preferred embodiments, the shape memory actuator is activated by applying and removing an electrical current to the shape memory element. For example, the drive mechanism may further include a power source coupled to the shape memory actuator to provide the electrical current to the shape memory actuator. Preferably, the preferred the shape memory actuator is formed from Nitinol material, with the preferred structure being a wire. In some embodiments, the drive mechanism utilizes less than three shape memory actuators, three force receiving members and/or three force applying members. In still other embodiments, the drive mechanism utilizes less than three shape memory actuators.
In a first embodiment of the present invention, the force receiving member is a guide and the force applying member is a carriage assembly. For instance, the guide is a shaft and the carriage assembly includes at least one pawl that is actuated to incrementally move the carriage assembly relative to the shaft. In further embodiments, the carriage assembly includes at least one pawl, a lever and a cam surface on one end of the lever, and the shape memory actuator is coupled to another end of the lever and actuated to move the cam surface of the lever against the at least one pawl to incrementally move the carriage assembly relative to the shaft. In another embodiment, the force receiving member is a gear, and the different position of the gear relative to the force applying member is an angular rotation. For example, the force applying member is a wire pawl that includes the shape memory actuator to pull upon the gear to cause the angular rotation. Alternatively, the force applying member is a bar that includes the shape memory actuator to push upon the gear to cause the angular rotation.
In another embodiment, the drive mechanism includes a guide, a carriage member and a shape memory actuator. The carriage member moves relative to the guide. The shape memory actuator is formed from a shape memory material and is operatively coupled to the carriage member. In addition, the shape memory actuator is activated to distort the shape memory actuator from a first shape to a second shape to move the carriage member relative to the guide. Further, the shape memory actuator is returned to the first shape from the second shape after the carriage has moved relative to the guide.
In further embodiment of the present invention, a drive mechanism for a medication delivery device includes a shaft, a carriage and a shape memory element. The carriage is coupled to the shaft to move relative to the shaft. The carriage includes a first pawl, a first resilient member, a second pawl and a second resilient member. The first pawl has a first end and a second end with a first bore. The first bore defines an opening between the first and second ends, and the edges of the first bore grasp the shaft when the first pawl is tilted. The first resilient member is coupled between the carriage and the first pawl to bias the first pawl to a first position relative to the shaft. The second pawl has a first end and a second end with a second bore. The second bore defines an opening between the first and second ends, and the edges of the second bore grasp the shaft when the second pawl is tilted. The second resilient member is coupled between the carriage and the second pawl to bias the second pawl to resist relative rearward movement of the carriage. The shape memory element activates the first pawl to move between the first position and a second position to move the carriage relatively forward, as the shaft is grasped by the edges of the first bore, when the first pawl is moved from the first position to the second position. The first resilient member is used to move the first pawl back to the first position after the carriage has moved relative to the shaft.
Other features and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings which illustrate, by way of example, various features of embodiments of the invention.